This being a holiday weekend, a young man’s heart turns to what? Ham Radio Antennas, of course!!!
Antennas 101: Short Course
In the event of an actual emergency, there are really only two antennas that work, provide reasonable gain and don’t require fancy ground systems to radiate pretty well.
HF Bands: On the 80-10 meter ham bands from 3.5 to 29 MHz, or so, the easiest antenna is called a “dipole.” Fed with a piece of coaxial cable, the approximate length of the antenna (overall) is 468 divided by the frequency in megahertz.
So, if you wanted an antenna to transmit at night on 75-meter ham band, say 3.8 Mhz (lower sideband voice), your antenna length would be 468/3.8, or about 133.7 feet, or turning the point-7 into inches, it’s be about 133-feet 8-1/2″ overall.
The VHF, 2-meter dipole for 147-MHz would be 468/147 or about 38.2 inches call it 19-inches either side of center and close enough. 2-Meter (VHF equipment) is much less “picky” about antennas.
One side of the coaxial cable is connected to one side of a center insulator, while the center to the other side. Now, all you need to do is hoist away into a tree or the 100-foot high ham radio tower and you will “own the band” because the higher an antenna is (at night) the better it generally works – at least up to several hundred feet.
“I don’t have a tower! What then?”
Ah…you have walked into my trap (now sprung) as I reveal a whole sub-culture of ham operators called “Launchers.”
“Launches of what?”
Why, antennas, of course, silly!
Concept: Shoot a fishing weight way up a treet and use fishing like to haul up heavier line, which is then used in turn to bring up the antenna. 500-foot rolls of Kevlar paracord on sale (look for 3/16ths if you can find and afford it) and your antenna problems are over.
Here’s your homework assignment for our next class:
- Visit the Joplin Amateur Radio club. For $50 bucks, you can buy a kit that will give you most of the parts needed to build an air-powered antenna launcher. The idea is simple enough: With some hollow PVC pipe, a couple of fittings, and some clever assembly you can build a device that will toss a good-sized fishing lure up into the 60-foot altitude range of whatever tree happens to be handy in your area. People who’ve been through REAL aftermath of major storms (remember their tornado in Joplin?) these folks know that when all else fails there’s Ham Radio. A visit to http://joplin-arc.org/antenna-launchers/ will bring you up to speed. Just realize, you’d still need to add more fishing line and a cheapo spinning reel plus extra “lures” and if you’re not perfectly sighted, hitting the lures with fluorescent orange won’t hurt, either. Tub of hot-set PVC glue and baddah-bing!
- For extra credit, you can visit where the “upper classmen” or this angle of the hobby hang out: http://www.antennalaunchers.com/antlaunching.html. What you will find is an incredible treasure trove of air-powered antenna launchers…and enough links to keep you from reading the rest of today’s discussion on advanced antenna concepts.
Why would anyone, other than a ham (and we’re half-crazy anyway, what with some of us being “digital humans” ahead of the herd, being able to push around Morse code which is no longer required for licensing) have to do with such air toys?
As the AntennaLaunchers site explains, they can also be used for such things as…
- “Cutting high tree branches using a pull-chain saw
- Deploying Safety Lines for roof, tree or tower work
- Putting climbing lines in place for treetop canopies
- Training dogs for fetching after a mild report
- Putting a temporary wire antenna part way up a tower without climbing
- Putting a line across a pond
- Fishing – Casting far out in the surf or lake”
Go read up on what they’re up to. Damn cool stuff. Why, you could launch a 150-foot high antenna into a giant pine by some lake and then blast out across the lake and troll for lunkers while owning the DX portion of 20-meters. Is this a grand science, or what?
Now that I’ve picked up over 1,000-feet of #14 stranded insulated wire (ugly brown is stealthy) for under $30 per 500 foot roll on special at the Zon, I’m hot to trot on a launcher for the fall. Since we have trees up in the 100-foot class around the property, what better tool to assemble an aluminum and copper “overcast” to convert our “tree farm” to mixed environmental and industrial use?
Antennas 605 Class: Mega-Tenna II
Yes, forget the two-legged dear-hunting this weekend, park the jet skis, and forget those idyllic rides down some 20-mile long stretch of warm water river with a dolly on one arm and a cold beer in the other… I mean seriously (or nearly so) How could anyone waste time like that when they could be modeling antennas?
Unthinkable the way some people squander life, ain’t it?
(Pauses to pry tongue from cheek…then continues…)
Modeling antennas is “thinking man’s chess” when comes to the honorable and ancient art of low-power, global radio communications.
Sure, anyone can talk on ham radio (anywhere pretty much, day or night, plus or minus a solar flare and depending on satellite use skills). It’s easy to hook up a computer and send pictures flying around the world with no internet. Especially if you know the secret to high antennas without climbing things. (See Antennas 101 above.)
Instead of nursing a tan in the wee hours (which has turned into a 3rd degree sunburn around then) or chasing this weekend’s new love of your life…why who wouldn’t jump at the chance to sit down in front of $5000 worth of radio gear and exchange pleasantries with some geezer in Australia or Russia?
Point is, as long as the world hasn’t blown up yet (give it time) ham radio is a sport. The post-nuke lifeline part comes later.
When it does?
You Need a Kick-Ass Antenna
Yes, even if you’re only prepping for a camping trip, a solid AM and shortwave portable can give you something interesting to do at night between “right-after the Viagra wears off” and before the hangover comes along…
Monster Antennas to the Rescue!
Radio Club Jeff and I had a conversation a few weeks back (best I can recall, remember there was some post-hernia oxycodone pain meds in the mix somewhere!) about antenna design. We exchanged views on “open wire feedlines.”
As you may be aware, the “usual” way to move a [radio signal] from a transmitter to [antenna] (or antenna-to-receiver) is employing coaxial cable. It looks like a piece of garden hose. Braid on the outside (one conductor) and then filled with insulation except for the very well-insulated center conductor.
The “best of the best” short of pressurized television transmitter feedline (made of economically irrational copper called Heliax cable – being filled with helium, but might as well be filled with “money”) is probably Times Cable LMR-400. If you’re buying, get the SF (super-flexible) version. It’s the modern-day, lower loss version of the 1950’s ancestor RG-8, which was in turn begat as an offspring of .mil spec RG-213. These are 50-ohm antenna cables. That’s it “impedeance”.
About here is where the transmission “line loss” discussion begins.
Think of impedance matching as electrically matching up “pipe sizes” and you’ll be in the ballpark. A 50 ohm transmission line feeding into an antenna with an impedance of 200 ohms will have a 4:1 mismatch.
These can be corrected with line transformers (current or voltage) under the heading “BALUN.” Short for “balanced to unbalanced.” A dipole antenna, being the same either side, likes a “balanced feed.” Since our coaxial cable is unbalanced (but so are we) the role of a BALUN is to convert 50-ohm unbalanced feet line to 200 ohm balanced output.
With ooaxial cable, as the impedance mismatch goes up, losses mount quickly.
Is a coaxial cable better than the old-school 2-wires just carefully spaced a few inches apart?
In fact, there’s a LONG discussion of the issue of coax’s greatness over on ham.stackexchange you might want to look at.
The bottom line seems to be that LMR-400 coax, which is what feeds the tri-band beam on the Ure tower and our previous Mega-Antenna I is hard to beat.
Unless you want to use the 40-meter band, that is. And that brings up the problem which drives us to shun the sun, cold brewskis and outdoor life on weekends like this. Mega Antenna II will bot get built by itself.
What we need to do first is come up with?
A (MA-II) Design Process
Coaxial cable does very well, with acceptable losses when properly terminated. (Matched-pipe sizes)
However, on the lower ham bands, it’s not uncommon to find a 150 (or larger) ohm antenna impedance across the 80-meter ham band. This 3 to 1 “Standing Wave Ratio” is a polite way of saying “loss.” High SWR on coax = Bad, very bad. Higher the ratio, worse the loss.
This is because many transmitters “dial-back” output power when the SWR (reflected power) rises over 2 or 3 to 1. My Yaesu FT-920, for example, rolls back to half power at a 3-1/2 to 1 SWR on the lower end of the 80-meter ham band.
Tube-type gear ain’t so picky. One reason we love the stuff. The high powered (tube-based) amp for this band (a Heathkit SB-220 with 2 Eimac 5-500Z’s of Johnson Thunderbolt with a pair of 4-400A’s depending on mood swings) is very forgiving as tubes are. The SB-220 will still push out 1,100 watts driven by my Kenwood TS-590S right up to the point where things arc at about a 4.5 to 1 SWR. (Be polite, don’t ask how I learned this…High power amp components can make small caliber noises when failure modes arrive…arcing, components blow up as loud as a .38 special with a small load, all teaching experienced hams calmness under fire. We keep an extinguisher handy for those, too…)
When 80 meter band conditions are crummy, and 20-meters is not open, that’s when the local “operating gulch” appears. The only 40-meter antenna I have is a 40-meter add-on to the beam up 65 feet on the tower. Works, match is narrow, band it’s not particularly effective, since it’s less than full size. When comes to antennas? Size matters…Bigger is Better, Higher is Better.
I Want It ALL
Who doesn’t? But what is the “right” antenna? The NEXT ONE, of course!
Back to Radio Jeff’s suggestion. “You know, people do just great with a good open-wire antenna tuner and just throw up a doublet antenna for whatever your lowest operating frequency will be and call it good…:”
As explains Wikipedia: “In the early days of radio, the thus-named Marconi (vertical) antenna (monopole) and the doublet (dipole) were seen as distinct inventions. Now, however, the “monopole” antenna is understood as a special case of a dipole which has a virtual element “underground”.
Solid advice from brother Jeff, so I ignored it. A simple doublet wouldn’t have any GAIN. And gain is like the holy grail of antenna design. That and bandwidth (and cost, and ease of construction, and can you get it past the wife..the cranky neighbors, the zoning department…See how complex antennas get?)
Antenna Addict Confessions
I’ve been fascinated for years with performance of a “Double Extended Zepp” antenna. Or is it an Extended Double Zepp? No two people agree.
Yes, the Zepp antennas were a variant of those antennas used on those Hindenburgy things that once flew more dependably than, oh, a 737 Max. The Extended Zepp and Double-Extended flavors and naming confusion came later.
Today, you can find the big brother to the simple “End-Fed Zepp” many places on the web. Damn fine antennas, these Double Extended Zepps (DEZ) because they have gain. Lots of it. In some directions they can nearly double your effective radiated power (ERP).
One draw-back is they’re not small. West Mountain Radio, which in addition to making dandy ham gear, has an online DEZ calculator. I put in a selection of 40-meter frequencies and decided something around 88-feet either side of the center insulator would be right.
Modeling a Benchmark Antenna
The simplest antenna for the 80-meter band would be a 60-foot, either side of center, dipole. To see how a 40 meter DEZ would perform on 80, we’d need to model both.
Here are the basic model of the benchmark – a simple dipole with an apex at 55 feet and the ends 66-feet out and 30-feet into trees:
This first model says “On 80 meters, most of the power will go up and then splash back down to earth – so it’s good for NVIS (near-vertical incidence skywave) short to medium-range work. Good for emergencies and yet you can do OK at night with it. Bettrer if an NVIS counterpoise (passive ground reflector) is included in the build.
The problem with this “half-wave dipole” is that it sucks in terms of efficiency when operated ay half its design frequency which is what happens on 7.15 MHz (40-meters):
At a glance (if you’re a radio engineer-in-training) you’d see that while on 80 meters you’ve got 6.31 db radiating for you, on 40 you’re under 5 db…so a loss of 1.31 db…but that’s only the beginning of the problems. Remember, the bigger the mismatch, the bigger the feedline loss.
On 80-meters, the benchmark dipole kills for low SWR – which falls to nearly-perfect at 3.6 MHz:
Thing is, its up around infinite on 40 meters. Dipoles are great either on one band or on their third harmonic. A 40-meter dipole at 7-MHz works fine on the 15-meter band (21-MHz).
Now Let’s Model the DEZ
The first thing we see is that the DEZ doesn’t have a particularly good SWR, either:
That looks terrible, EXCEPT that with open wire (ladder line) who cares about losses? There’s almost no loss. A single decibel, maybe? But in return OMG look at the gain figure that more than counter-balances that tiny loss!!
Compared with an 80-meter dipole operating on its second harmonic, the DEZ essentially doubles the ERP )*effective radiated power). So a 100-watt transmitter acts like a 200-watt transmitter. Or, on voice, 15-hundred watts PEP talk power (Peak Envelope Power or ERP) just went to 3-kilowatts. Yeah baby…let’s chat up Down Under and give them boys in Siberia a holler, too!
What’s also interesting is that on 80-meters, this 88-foot either side of center also looks (even after ladder line losses) like it will smoke the benchmark on all but exactly the matched SWR point:
Best part of the magic? I can orient this thing to take advantage of its gain to bump signals up to the Pacific Northwest where my buddy the Major is and my son George II, KF7OCD who’s also an extra class ham.
All of which sounds ideal, doesn’t it? “Gimme big lobes, baby!” Well, it’s not quite perfect. Because?
Toss in $300 for a Special Tuner
I had to “go fishing” on eBay for an old school super antenna tuner. One that was designed to handle the power involved and has a good track record, is solidly built and so forth.
Essentially, you have two choices on antenna tuners: You can trust an antenna tuner that uses the “new-fangled” ferrite core inductors (to get a lot of inductance out of not very much wire). This involves ferrite cores of the right blend, size, and wire turns ratios… OR you can old-school it.
There is exactly ONE old school tuner worth working into the modern ham station. That’d be the Johnson Kilowatt MatchBox.
I mean besides the fact it’s a design compliment to the equally old-school Johnson Thunderbolt Amplifier I restored back in 2018…which it was designed to mate.
With ONE eBay MatchBox in hand, it was time to rethink 1960’s engineering design. Now days, most radios are transceivers with antenna in-out switching done inside the amplifier. Simple stuff.
Back then? There is a ton of switching included in the MatchBox. Before putting up this new antenna, needed to “go through” the design and simplify it a great deal:
I have color-coded the strategy for MatchBox #1.
Yellow are connectors that need to be replaced and switches that need to be thoroughly cleaned.
The black wire from the yellow connector on the left will run both the receive and transmit signal through the same main line rather than using a special coupling link for the receiver. No longer needed. Back in early MatchBox times, 300-ohm receiver front-ends were common. Nowadays, 50-ohms is standard, so no point in keeping the additional coil tap and that let’s us ditch a noisy (old) relay.
Key, though is keeping the modifications easily reversible, should someone ever want to put the Matchbox back to “stock.” Some oldegenarians like the lights to dim and relays thwack loudly when “the Big Switch” is thrown. Personally, I find the mercury-whetted relay in my Hallicrafters T.O. Morse keyer a bit loud… but to each their own.
Oh yeah: the green marks show where the split-stator variable capacitors will be spiffed up so they don’t make any noise when tuned. That should have done it.
But, turns out, when I opened MatchBox #1, a 60-year old design fault came to light. EF Johnson has run a solid (silver coated) wire from the output capacitor to the coaxial line out on the back of the unit. Over the years, with the insides inspected by “golden screwdriver” award-winners, the solder connection to the variable (coulpling) capacitor had failed.
Replaced it with flexiblke braid so there’s a tiny bit of “give” to it and now it’s ready for another 50-years.
With the arrival this week of a second Kilowatt MatchBox (#2) I should be able to gin-up a second DEZ monster spaced back from the first one. Once both are going, not sure what the gain will be like, but wow…what a dream antenna for point (Texas) to point (Washington) communications on 40 and 80- meters.
The Open Ladder Routing Problem
That leaves only a couple of problems left but the biggest is building up the open-wire line. There was a “kit” on eBay for reasonable a while back for a 100-foot build-it-yourself which came with the 200-feet or wire and the spreaders pre-drilled. Just assemble and off you go.
Well…sort of. The problem is getting the “right” weather proof routing into the office. Looks like that will be two 3/8ths inch plastic pipes on 3-1/2 inch centers through the wall. But the competing design is lengths of 1/4″ brass treaded rod with “banana jack” connectors. That’d work, too.
My original thought was drilling the window in my office with a diamond bit drill set. But, before starting, I got to wondering if the glass was tempered or annealed. I put it in 13-years ago and the window was recycled out of an old storm door…
Good thing I checked! Drilling – even with glass oil and diamond bits – shatters tempered or annealed glass with a high-enough frequency that I chickened-out. (If I was any more cowardly, I could be an Inspector General…)
The other remaining problem is deciding which ham radio stations to leave set up and which ones to sell off. Damn hard choice. It’s not unlike the guy who restores cars only to wake up one morning with a Porsche, a Vette, a Pantera, and Austin-Healy 3000, and a GT-500 plus a Viper. How the hell do you decide? All of the Above?
Same problem must be true for all hobbies held long enough. At last count my consiglieri still has three sailboats…so my thinning-down the herd problem is not unique…I’ll sell a radio when he sells a boat, maybe…use him for a benchmark…
Off to the soldering gun…but for more, visit the W5DXP website where he’s got a lower impedance (works with coax) version of the DEZ – or is it EDZ? Since he calls his invention the The Half-Extended Double Zepp (HEDZ). My dimensions (without heavy planning) will be pretty close to what he’s showing.
My hope is to cobble up something that will come close to hitting the 600 ohm ladder line and with the MatchBoxes, a pair of phased DEZ’s wide-spaced oughta play really well. Some eHam.net comments here are of interest, too.
Write when you get rich, or if you get DX Century Club on QRP (low power, 100 countries confirmed). THAT would be impressive.